This proposal seeks to investigate how various components in colostrum, such as antigens and antibodies, might alter the subsequent immune responsiveness of the nursing newborn. It is particularly concerned with the idea that neonatal gut contact with antigens may lead to a state of immunological tolerance to these antigens. The role of suppressor cells induced by this colostral route of contact and possible defects in B-cell development are to be examined. Further it is proposed to study the mechanism of transport of substances from serum into the colostrum.